Thermoelectric device and a method of manufacturing thereof

ABSTRACT

A method of making a thermoelectric device comprises forming electrodes on a surface of a first substrate and on a surface of a second substrate. Thereafter, a P-type thermoelectric material plate is bonded to the surface of the first substrate having the electrodes, and an N-type thermoelectric material plate is bonded to the surface of the second substrate having the electrodes. Each of the thermoelectric material plates are then processed by cutting and removing portions thereof to form P-type and N-type thermoelectric material chips bonded to the first and second substrates, respectively. Thereafter, the N-type thermoelectric material chips of the second substrate are bonded to the electrodes of the first substrate, and the P-type thermoelectric material chips of the first substrate are bonded to the electrodes of the second substrate to form PN-junctions between the first and second substrates.

BACKGROUND OF THE INVENTION

1. Field of the Invention!

The present invention relates to a thermoelectric device and a method ofmaking thereof which make possible electric generation by temperaturedifference (thermal power generation) by the Seebeck effect andthermoelectric cooling and heat generation by the Peltier effect.

2. Prior Art!

A thermoelectric device is made by bonding a P-type thermoelectricmaterial and a N-type thermoelectric material via an electricallyconductive electrode such as a metal to thereby form a couple of PNjunctions. The thermoelectric device generates thermal electromotiveforce based on the Seebeck effect by a temperature difference appliedbetween ends of the junction couple. Therefore, it has applications fora power generating device and conversely, a cooling device and a finetemperature control device utilizing the so-called Peltier effect inwhich one side of a junction is cooled and the other side generates heatby making electric current flow in the device and the like.

Generally, a thermoelectric device is used as a module in which aplurality of couples of PN junctions are connected in series to promoteits function. In the structure of this module pieces of P-type andN-type thermoelectric materials (called thermoelectric material chip)having a shape of a rectangular parallelopiped of which size ranges fromseveral hundred μm to several mm are interposed by two sheets ofelectrically insulative substrates of alumina, aluminium nitride or thelike, the P-type thermoelectric material chips and N-type thermoelectricmaterial chips are PN-coupled by electrodes of an electricallyconductive substance such as a metal formed on the substrates and at thesame time the thermoelectric material chips are connected in series bythese junctions.

FIG. 16 illustrates views showing an arrangement of electrodes ofsubstrates and thermoelectric material chips at a section cut in adirection in parallel with the substrates and respective sections in adirection orthogonal to the substrates of a conventional thermoelectricdevice (hereinafter called a thermoelectric device including a module inwhich the above-mentioned plurality of thermoelectric chips arearranged) having such a structure. FIG. 16A is a view showing anarrangement of electrodes and thermoelectric material chips on thesubstrate at a section in parallel with the substrates of theconventional thermoelectric device. In other words, it is a perspectiveview for indicating the arrangement of the electrodes and thethermoelectric material chips from above the substrate. An electrodepattern shown by bold lines indicates an electrode 161 of a topsubstrate whereas an electrode pattern shown by dotted lines indicatesan electrode 162 of a bottom substrate. Further, a hatched quadrangle atthe inside of a portion in which the electrode 161 of the top substrateintersects with the electrode 162 of the bottom substrate indicates aportion in which a P-type thermoelectric material chip 163 or a N-typethermoelectric material chip 164 is disposed. FIGS. 16B, 16C, 16D areviews showing respective longitudinal sections of FIG. 16A taken alonglines X1--X1', X2--X2' and Y1--Y1'. As is apparent from FIG. 16, thearrangement of the thermoelectric material chips in the conventionalthermoelectric device is in a lattice form arranged on the substrate andthe P-type thermoelectric material chips and the N-type thermoelectricmaterial chips are always arranged alternately in respective rows (Xdirection and Y direction in FIG. 16A) constituting the lattice.

An explanation will be given of a method of making the conventionalthermoelectric device comprising a plurality of the thermoelectricmaterial chips as follows.

FIG. 17 illustrates views showing an outline of working thermoelectricmaterial in manufacturing the conventional thermoelectric device bylongitudinal sections thereof. FIG. 17A shows a section of athermoelectric material 171 which has been worked in plate-like form orrod-like form. Layers 172 are formed for soldering by Ni etc. on bothfaces of the thermoelectric material to be bonded to the substrates by aplating method (FIG. 17B). Next, P-type and N-type thermoelectricmaterial chips 173 each having the layers 172 for soldering on its bothfaces are formed by cutting the thermoelectric material (FIG. 17C).

Successively, each of the thermoelectric material chips formed as aboveis disposed on a predetermined electrode on the substrate by using jigsor the like and a bonding is performed thereby forming thethermoelectric device. FIG. 18 illustrates views showing a conventionalmethod of manufacturing a thermoelectric device by using thethermoelectric material chips and substrates provided with electrodes.FIG. 18A shows relationship between the substrates 181 andthermoelectric material chips 182 before bonding. Electrodes 183 forforming PN junctions and bonding materials 184 for bonding thethermoelectric material chips 182 to surfaces of the substrates areformed on the substrates 181 in layers. FIG. 18B shows a longitudinalsectional view in which a thermoelectric device 185 is formed by bondingthe respective portions.

Each thermoelectric material chip used for a thermoelectric device is arectangular parallelopiped having sides with a size ranging from severalhundred μm to several mm. However, in recent years, in an device used ataround room temperature under a temperature difference of several tensdegrees it has high function when its size and thickness ranges fromseveral tens to several hundred μm. For example, such a content isdescribed in, The "Transaction of the Institute of Electronics,Information and Communication Engineers C-II, Vol. J75-C-II, No. 8, pp.416-424(JAPAN)" (in Japanese) and the like, while importance of designwith respect to heat is set forth in the same paper.

Further, the number of couples of thermoelectric material chips in onethermoelectric device has been several hundreds at most and its densityhas been approximately several tens couples/cm². However, to increasethe number of couples of thermoelectric material chips is one of veryimportant factors in promoting its function and expanding itsapplication. Especially, in power generation using a small temperaturedifference, generated electromotive force is in proportion to the numberof couples of thermoelectric material chips and therefore, it isdesirable to increase as many as possible the number of thermoelectricmaterial chips connected in series in a thermoelectric device togenerate a high voltage. Furthermore, also in case where athermoelectric device is used as a cooling device or a temperaturecontrolling device, electric current flowing in an device is enhancedwhen the number of thermoelectric material chips connected in series issmall and it is necessary to enlarge wirings or to enlarge powersources. Accordingly, it is desirable to arrange as many thermoelectricmaterial chips as possible in series.

As state above, miniaturizing, thinning, thermal design and an increasein the number of the couples of the thermoelectric material chipsconnected in series in a single thermoelectric device amount to highfunction of the thermoelectric device and at the same time are becomingpoints of expanding its application.

However, in making thermoelectric devices having the conventionalstructure shown in FIG. 16 by the manufacturing method shown in FIG. 17and FIG. 18, it is necessary to handle the thermoelectric material chipsone by one and there is a limitation for reducing the size of the chipand the size of the device considering the operational performance andthe working accuracy. Especially, thermoelectric materials having goodfunction including Bi-Te series materials, Fe-Si series material and thelike are substances having low mechanical strength. Therefore, in makinga thermoelectric device in which the size of the thermoelectric materialchip is no more than several hundreds μm or the number of chips isextremely large, the handling of the thermoelectric material isdifficult and it is difficult to make thermoelectric device having theconventional structure by the conventional manufacturing method.

Further, when a large number of thermoelectric elements are line-up inseries with one another, if there is a discontinuity even at just onepart of the electrodes or the thermoelectric materials, the function ofthe device is impaired. This problem lowers the manufacturing yield andat the same time is considered important from the point of view of cost.

It is an object of the present invention to provide a thermoelectricdevice which is small in scale and high in function and a method ofmaking thereof by reducing the size of the thermoelectric material chipsand increasing the number of thermoelectric material chips per unit area(chip density).

SUMMARY OF THE INVENTION

The present invention allows to adopt a new manufacturing method byimproving the arrangement of thermoelectric material chips in theconventional thermoelectric device on substrates and provides athermoelectric device in which the size of thermoelectric material chipsis reduced and the chip density is enhanced.

Outline of the present invention is as follows.

The first object of the invention is to provide a thermoelectric devicecomprising two sheets of substrates each having electrodes and at leastone of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-coupled via theelectrodes, wherein a sectional shape of each of the thermoelectricmaterial chips cut by a plane in parallel with the two sheets ofsubstrates is quadrangular and the thermoelectric material chips andelectrodes for PN junctions are arranged such that a positional anddirectional relationship between a straight line connecting centers ofquadrangles of the electrically coupled P-type and N-type thermoelectricmaterials and each of four sides constituting the quadrangle that is thesectional shape of each thermoelectric material chip forming a couple ofPN junction is not in an orthogonal or parallel relationship.

In other words, above mentioned "positional and directionalrelationship" means that a distance between the centers of quardranglesof the electrically conpled P-type and N-type thermoelectric materialchips is ranged from a half to equal distance between the centers ofquadrangles of the same type chips which are disposed mostly closed.

Another object of the invention is to provide a thermoelectric devicecomprising two sheets of substrates each having electrodes and at leastone of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-coupled via theelectrodes, wherein a sectional shape of each of the thermoelectricchips cut by a plane in parallel with the two sheets of substrates isquadrangular, at the same time the thermoelectric material chips arearranged in a lattice form on the substrates in side directions of aquadrangle that is the sectional shape of each of the thermoelectricmaterial chips, the P-type thermoelectric material chips and the N-typethermoelectric material chips are alternately arranged at a first sideconstituting the lattice arrangement of the chips and rows of only theP-types thermoelectric material chips or only the N-type thermoelectricmaterial chips are alternately arranged at a second side thereof.

According to the thermoelectric device described above, degree offreedom of design and manufacturing method of thermoelectric deviceshaving a plurality of PN junctions can be broadened by the positionalrelationship between the P-type thermoelectric material chips and theN-type thermoelectric material chips as well as the directionalrelationship between the P-type and N-type thermoelectric material chipsand electrodes for PN junctions, and therefore, a thermoelectric devicecomprising thermoelectric material chips of several hundred μm or lesscan be manufactured.

Another object of the invention is to provide the thermoelectric deviceaccording to above mentioned device, wherein dummy thermoelectricmaterial chips which are not electrically connected are bonded andincluded in the device other than the thermoelectric material chipshaving PN junctions and constituting the device.

According to the thermoelectric device described above, the mechanicalstrength of the thermoelectric device can be enhanced by bonding theelectrically isolated thermoelectric material chips to the substrates.

Another object of the invention is to provide a thermoelectric device asset forth above wherein the thermoelectric device has electrodes each ofwhich is connected with a plurality of chips of a same type among theelectrodes formed on the substrates for forming couples of PN junctions.

According to the thermoelectric device described above, thethermoelectric material chips having a same type are bonded to anelectrode for PN junction and therefore its mechanical strength isenhanced and the device can achieve the function even if one of them isdestroyed.

Another object of the invention is to provide a thermoelectric devicecomprising two sheets of substrates each having electrodes and at leastone of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-coupled via theelectrodes, wherein a sectional area or width of each of thethermoelectric material chips is changed in a width thereof in adirection orthogonal to the substrate.

According to the thermoelectric device described above, in case wherethe Peltier effect is utilized, it is possible to prescribe a locationof generating Joule heat caused by flowing current depending on thesectional shape. Further, in making the thermoelectric device, athermoelectric device comprising thermoelectric material chips ofseveral hundreds μm or less can be manufactured and its yield can bepromoted.

Another object of the invention is to provide a thermoelectric devicecomprising two sheets of substrates each having electrodes and at leastone of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-coupled via theelectrodes, wherein structures are provided proximate to portions of asurface of at least one of the substrates at which the thermoelectricmaterial chips and the substrate are bonded.

According to the thermoelectric device described above, a bondingmaterial such as solder is prevented from oozing in bonding thesubstrates to the thermoelectric materials and at the same time thepositioning of the thermoelectric materials to the substrates isfacilitated by the structures proximate to bonding portions of thesubstrates.

As another object of the invention, the sizes or shapes of thestructures proximate to the bonding portions on a single substrate aredifferent depending on the portions in which the P-type thermoelectricmaterial chips or the N-type thermoelectric material chips are disposedand therefore, the bonding can be performed without taking wrong typesof the thermoelectric materials. Further, when the thermoelectric deviceis manufactured by a step of performing PN junction by firstly bondingthe P-type thermoelectric material chips and N-type thermoelectricmaterial chips to the respectively separate substrates and thereafter byopposing the substrates, the positional-accuracy of bonding can bepromoted by making smaller the structures used for positioning in thefirst bonding, allowance is provided to the positioning in the secondbonding (PN bonding) and at the same time the bonding material can beprevented from oozing by making larger the structures used in thepositioning therefor.

As another object of the invention, the sizes or shapes of thestructures provided on the substrates are different with respect to asame thermoelectric material chip depending on the two sheets ofsubstrates and therefore, the bonding can be performed without takingwrong types of thermoelectric materials. Further, in case where thethermoelectric device is manufactured by the step of performing PNjunction by firstly bonding the P-type thermoelectric material chips orthe N-type thermoelectric material chips to the respectively differentsubstrate and thereafter opposing the substrates, the positionalaccuracy of bonding can be promoted by making smaller the structuresused for positioning in the first bonding, allowance is provided to thepositioning in the second bonding (PN bonding) and at the same time thebonding material can be prevented from oozing by making larger thestructures used in the positioning therefor.

As another object of the invention, the structures proximate to thebonding portions on the substrates are made of a high polymer materialhaving poor thermal conductivity and therefore, heat can be preventedfrom flowing from a high temperature end to a low temperature end of thethermoelectric device by which the function of the device is notlowered.

As another object of the invention, the structures proximate to thebonding portions on the substrates are made of a cured photosensitiveresin by which a miniaturization can be achieved by photolithography andtherefore, the structures are effectively operated in manufacturing athermoelectric device comprising thermoelectric material chips ofseveral hundreds μm or less.

Another object of the invention is to provide a thermoelectric devicecomprising two sheets of substrates each having electrodes and at leastone of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-bonded via theelectrodes, wherein at least one of the two sheets of substrates aremade of silicon.

According to the thermoelectric device described above, a fine workingcan be performed by using silicon for the substrates and therefore, athermoelectric device comprising thermoelectric material chips ofseveral hundred μm or less can be manufactured. Further, the thermalconductivity of silicon is higher than that of ceramics such as aluminaas well as higher than that of a metal such as aluminium at lowtemperatures, an effective absorption of heat from the substrates can becarried out and therefore, the function of the thermoelectric device canbe promoted.

Another invention is to provide a thermoelectric device comprising twosheets of substrates each having electrodes and at least one of couplesof P-type and N-type thermoelectric material chips interposed by the twosheets of substrates and PN-coupled via the electrodes, whereincompositions of bonding materials for bonding the thermoelectricmaterial chips to electrodes formed on the two sheets of substrates inbonding thereof on at least one of the two sheets of substrates arerespectively different depending on a difference in types of thethermoelectric material chips.

According to the thermoelectric device described above, in the bondingfor forming the couples of PN junctions after bonding the P-typethermoelectric material chips and the N-type thermoelectric materialchips to the respective separate substrates, the bonding can befacilitated.

Another invention is to provide a thermoelectric device comprising twosheets of substrates each having electrodes and at least one of couplesof P-type and N-type thermoelectric material chips interposed by the twosheets of substrates and PN-coupled via the electrodes, wherein thethermoelectric material chips and first electrodes formed on the twosheets of substrates for forming PN junctions are bonded throughprotruded second electrodes.

According to the thermoelectric device described above, the PN junctionscan easily be formed by the protruded second electrodes and therefore, amethod of making a thermoelectric device comprising thermoelectricmaterial chips having a size of several hundred μm can be adopted.

As another object of the invention, the protruded electrodes areprovided with a solder bump structure formed on the thermoelectricmaterials and therefore, even if heights of the P-type thermoelectricmaterial chips and the N-type thermoelectric material chips are madedifferent, the difference in the heights can be canceled by the solderdue to melting of solder in bonding and the thermoelectric element caneasily be manufactured.

Another object of the invention is to provide electrodes connecting tothe electrodes for PN junctions formed on the substrates sandwiching thethermoelectric material chips so as to connect the chips in serieswithin the device. These electrodes not only junction the thermoelectricmaterial chips but also establish connection with outside device or withother electrodes within the device.

By providing above mentioned electrodes, when there is a defect such asa discontinuity in the thermoelectric material chips within the deviceor the electrodes for PN junctions on the substrate at the time ofdevice assembly or after module assembly, if the electrodes areelectrically connected so as to avoid the electrically defective portionit is possible to allow the apparatus to function as a device althoughthe performance of the entire apparatus is reduced by the function ofthe removed portion. Also, by using these electrodes as inspectionelectrodes, the existence and position of defects such asdiscontinuities within the module can be identified. The electrodes ofthe present invention can therefore be used as input/output electrodes.

Another invention is to provide a method of making a thermoelectricdevice comprising two sheets of substrates each having electrodes and atleast one of couples of P-type and N-type thermoelectric material chipsinterposed by the two sheets of substrates and PN-coupled via theelectrodes wherein P-type and N-type plate-like or rod-likethermoelectric materials (hereinafter, plate-like or rod-likethermoelectric materials are called wafer-like thermoelectric materialsor thermoelectric material wafers) are bonded to each of the twoseparate sheets of substrates having predetermined electrodes to form PNjunctions. Next, portions of each of the bonded thermoelectric materialwafers are cut and eliminated in accordance with the necessity to showup electrodes to which thermoelectric material chips having respectivedifferent types are to be bonded. At this occasion, portions of thesubstrate or the electrodes are cut in accordance with the necessity. Bythese steps two sheets of the substrates are formed; in one of thesubstrates, the P-type thermoelectric material chips are bonded to thepredetermined electrodes and the electrodes to which the N-typethermoelectric material chips are to be bonded, come into view on itssurface, and in the other one of the substrates, the N-typethermoelectric material chips are bonded to the predetermined electrodesand the electrodes to which the P-type thermoelectric material chips areto be bonded, come into view on its surface. Next, with respect to thetwo sheets of the substrates, their faces bonded with the thermoelectricmaterial chips are opposed, the respective thermoelectric material chipsand the electrodes of the substrates are positioned to predeterminedlocations and the distal ends of the respective thermoelectric materialchips and the electrodes for PN bonding on the substrates are bondedwhereby couples of PN junctions interposing the electrodes of a metal orthe like are formed and the thermoelectric device is finished.

According to the method of making a thermoelectric device describedabove, after separately bonding the P-type and N-type thermoelectricmaterial wafer respectively and separately to the two sheets ofsubstrates each of which is previously provided with predeterminedelectrode wirings for forming the PN junctions, predetermined portionsof the bonded thermoelectric material wafers are cut and eliminatedthereby forming thermoelectric material chips bonded to the substrates.At this instance, the electrodes to be bonded to the thermoelectricmaterial chips of different types show up. The substrate in a state inwhich the P-type thermoelectric material chips are bonded thereto andthe substrate in a state in which the N-type thermoelectric materialchips are bonded thereto both formed thereby are opposed and bondedtogether at predetermined locations by which the thermoelectric devicecan be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing outlook of a thermoelectric device according tothe present invention.

FIGS. 2A-B illustrate views showing sections of major portions takenalong lines A--A' and B--B' of FIG. 1.

FIG. 3 is view showing a relationship between arrangement ofthermoelectric material chips and electrodes of a thermoelectric deviceshown in EMBODIMENT-1 of the present invention.

FIGS. 4A-E illustrate views showing outline of steps of manufacturingthe thermoelectric device according to the EMBODIMENT-1 of the presentinvention.

FIG. 5 is a view showing a relationship between arrangement ofthermoelectric material chips and electrodes of a thermoelectric deviceaccording to EMBODIMENT-2 of the present invention.

FIGS. 6A-F illustrate views showing outline of steps of manufacturing athermoelectric device according to EMBODIMENT-2 of the presentinvention.

FIGS. 7A-E illustrate views showing outline of steps of manufacturing athermoelectric device according to EMBODIMENT-3 of the presentinvention.

FIGS. 8A-F illustrate views showing outline of steps of manufacturing athermoelectric device according to EMBODIMENT-4 of the presentinvention.

FIGS. 9A-B illustrate views showing sections of the thermoelectricmaterial wafer after a grooving step among steps of manufacturing thethermoelectric device according to EMBODIMENT-4 of the presentinvention.

FIGS. 10A-B illustrate views showing sections of major portions after acutting and eliminating step among steps for manufacturing thethermoelectric device according to EMBODIMENT-4 of the presentinvention.

FIG. 11 is a view showing a finished section of the thermoelectricdevice according to EMBODIMENT-4 of the present invention.

FIG. 12 is a sectional view of a thermoelectric device having thestructure related to the thermoelectric device of EMBODIMENT-4 of thepresent invention.

FIGS. 13A-E illustrate views showing outline of steps of manufacturing athermoelectric device according to EMBODIMENT-5 of the presentinvention.

FIGS. 14A-E illustrate views showing outline of steps of manufacturing athermoelectric device according to EMBODIMENT-6 of the presentinvention.

FIG. 15 is a view showing a relatioship between arrangement ofthermoelectric material chips and electrodes of a thermoelectric deviceaccording to EMBODIMENT-7 of the present invention.

FIGS. 16A-D illustrate views showing a relationship between arrangementof thermoelectric material chips and electrodes of a conventionalthermoelectric device.

FIGS. 17A-C illustrate views showing outline of working thermoelectricmaterial in manufacturing the conventional thermoelectric device in itslongitudinal sectional view.

FIGS. 18A-B illustrate views showing a method of making the conventionalthermoelectric device wherein the thermoelectric device is manufacturedby using thermoelectric material chips and substrates provided withelectrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed explanation will be given of the present invention based onembodiments in reference to the drawings.

EMBODIMENT-1

FIG. 1 is a view showing appearance of a thermoelectric device accordingto the present invention. The basic structure of a thermoelectric device11 shown in FIG. 1 comprises substrates 12, P-type thermoelectricmaterial chips 13, N-type thermoelectric material chips 14 andelectrodes 15 for PN junction. FIG. 2A and FIG. 2B are views showingsections of major portions taken along lines A--A' and B--B' of FIG. 1showing appearance of the thermoelectric device, respectively.

In the sectional views of FIG. 2, in addition to the major portions ofthe thermoelectric device, structures 23 of the present invention areformed on the substrates 21 at the surroundings of bonding portions. InFIG. 2A that is a sectional view taken along the line A--A' of FIG. 1,the P-type thermoelectric material chips and the N-type thermoelectricmaterial chips are arranged alternately whereas in FIG. 2B that is asectional view taken along the line B--B' of FIG. 1, only P-typethermoelectric material chips or N-type thermoelectric material chipsare arranged. FIG. 3 is a perspective view showing an electrode patternand a positional relationship among the thermoelectric material chipsviewing the thermoelectric device of FIG. 1 from above. (Appearance andconcept are shown in FIG. 1, FIG. 2 and FIG. 3 and dimensions, a numberof the thermoelectric material chips and the like are determined inaccordance with the purpose). In FIG. 3, among lines showing electrodes,bold lines show electrode patterns 32 of a top substrate and dottedlines show electrode patterns 33 of a bottom substrate. Incidentally,the expression of top substrate or bottom substrate is for convenienceof explanation and naturally, any substrate can be a top or bottom onein the thermoelectric device. Further, quadrangles having two kinds ofhatched lines respectively show a P-type thermoelectric material chip 34and a N-type thermoelectric material chip 35.

An explanation will be given of a thermoelectric device and a method ofmaking thereof according to the present invention having such astructure with respect to a small-scaled thermoelectric device in whichthe size of the thermoelectric material chip is 100 μm.

As thermoelectric material, a sintered body of Bi-Te series materialthat is excellent in properties around room temperature was used. Asmain characteristics of the thermoelectric material, in P-type, theSeebeck coefficient was 205 μV/deg, the specific resistivity was 0.95 mΩcm and the heat conductivity was 1.5 W/m·deg whereas in N-type, theSeebeck coefficient was 170 μV/deg, the specific resistivity was 0.75 mΩcm and the heat conductivity was 1.5 W/m·deg. As material for thesubstrate, a silicon wafer having the thickness of 300 μm that waselectrically insulated by thermally oxidizing the surface was used. Withrespect to the size of the element and the like, the height of thethermoelectric material chip was 500 μm, the shape of a section of thethermoelectric material chip in parallel with the substrate was a squarehaving a length of a side of 100 μm as mentioned above, a distancebetween nearest thermoelectric material chips of a same type in FIG. 3was 200 μm (300 μm in center distance), a distance between nearestthermoelectric material chips of different types was 70 μm (300/√2=about210 μm in center distance) and a number of element couples arranged in asingle device in series was 125.

FIG. 4 illustrates views showing outline of steps for making thethermoelectric device of this embodiment. As shown in FIG. 4, the methodof making is grossly classified into five steps. An explanation will begiven thereof in due order.

In a bump forming step (A), a photoresist having the thickness of 50 μmwas coated on both faces of respective thermoelectric material wafers 40of P-type and N-type having the thickness of 500 μm and made of Bi-Teseries sintered bodies. A resist layer having circular openings eachhaving the diameter of opening of 90 μm, the arrangement of which was ina desired pattern, was formed by exposing and developing thephotoresist. The desired pattern was determined based on the abovedimensions to be conformed to the arrangement of the thermoelectricmaterial chips specified in FIG. 3. Next, after cleaning by an acid orthe like, a nickel plating of 40 μm was performed on the openings by anelectric plating method to form so-called nickel bumps. Next, a solderplating was performed on the nickel layer similarly by an electricplating method to form a solder layer of 30 μm. The solder plating wasperformed to form a solder of tin and lead having a composition ratio of6:4. Next, after removing the photoresist, a rosin group flux was coatedon the solder-plated layer, and a reflow treatment was performed at 230°C. by which spherical solder bumps 41 having the diameter ofapproximately 100 μm could have been formed on the both faces of thethermoelectric material wafer 40.

In an electrode forming step (B), films of chromium, nickel and gold inthis order from the substrate respectively having the thicknesses of 0.1μm, 3 μm and 1 μm were formed by a sputtering method on the surface of asilicon wafer substrate 42 having the thickness of 300 μm on which anoxide layer of 0.5 μm was formed by thermal oxidation. Next, electrodes43 were formed on the top and bottom substrates by photolithographyconforming to the electrodes pattern of FIG. 3. Further, two kinds ofdoughnut-shaped structures 44 of a polyamide group photoresist wereformed by photolithography at the surroundings of portions thereof towhich the P-type thermoelectric material and the N-type thermoelectricmaterial were bonded through the solder bumps. With respect to the sizeof the structure 44 comprising the polyamide group photoresist, in thetwo sheets of substrates constituting the thermoelectric device, theinner diameter of the doughnut shape was 120 μm the outer diameter was150 μm the height was 30 μm at a position where the P-typethermoelectric material chip was disposed and the inner diameter was 140μm, the outer diameter was 170 μm and the height was 30 μm at a positionwhere the N-type thermoelectric material chip was disposed in onesubstrate, whereas in the other substrate, the inner diameter was 140μm, the outer diameter was 170 μm and the height was 30 μm at a positionwhere the P-type thermoelectric material chip was disposed and the innerdiameter was 120 μm, the outer diameter was 150 μm and the height was 30μm at a position where the N-type thermoelectric material chip wasdisposed.

In a bonding step (C), the thermoelectric material wafer 40 having thebumps 41 formed in the bump forming step (A) was opposed to thesubstrate 42 having the electrodes 43 and the doughnut-shaped structures44 in the vicinity of the bonding portions formed by the electrodesforming step (B), predetermined positioning was performed and thethermoelectric material wafer 40 and the substrate 42 were bonded bymelting the solder. Further, in the bonding of the P-type thermoelectricmaterial wafer to the substrate, the solder bumps formed on the surfaceof the P-type thermoelectric material wafer were inserted into theinside of the smaller doughnut-type structures having the inner diameterof 120 μm, the outer diameter of 150 μm and the height of 30 μm whichhad been formed on the substrate thereby positioning the thermoelectricmaterial wafer 40 to the substrate 42. Similarly, in bonding the N-typethermoelectric material wafer to the substrate, the solder bumps formedon the surface of the N-type thermoelectric material wafer were insertedinto the smaller doughnut-shaped structures having the inner diameter of120 μm, the outer diameter of 150 μm and the height of 30 μm which hadbeen formed on the substrate thereby positioning the thermoelectricmaterial wafer 40 to the substrate 42. In this procedure, smaller onesof the doughnut-shaped structures having two kinds of sizes which hadbeen formed on the substrate in bonding the thermoelectric materialwafer 40 to the substrate 42 to dispense with incorrect bondingpositions and to promote mutual positioning accuracy.

In a cutting and eliminating step (D), portions of the thermoelectricmaterial wafer 40 bonded to the substrate 42 were formed intothermoelectric material chips 45 bonded to the substrate 42 by cuttingand eliminating other portions of the thermoelectric material wafer. Atthis instance, portions of the substrate 42 or the electrodes 43 mightsimultaneously be cut and eliminated in accordance with the necessity.In this embodiment, the cutting and eliminating step (D) was performedby using a dicing saw that was used in cutting silicon semiconductorsand the like. A blade having a thickness of 200 μm was used in thecutting and eliminating step. The thickness of the blade was selectedunder conditions wherein the length of the side of the thermoelectricmaterial chip 45 in this embodiment was 100 μm, the center distancebetween the nearest thermoelectric material chips of a same type was 300μm and the thermoelectric material chips of different types were bondedin the positional relationship prescribed in FIG. 3. The cutting andeliminating of unnecessary portions of the thermoelectric material wasperformed at central portions between the solder bumps 41 and at thesame time the height of the blade was adjusted so as not to destruct theelectrodes 43 on the substrate by utilizing a gap between thethermoelectric material wafer 40 and the substrate 42 comprising nickelbumps having the height of 40 μm. With respect to the thermoelectricmaterial of each type, the substrate 42 bonded substantially with 125pieces of the thermoelectric material chip 45 was manufactured bylongitudinally and transversely cutting and eliminating other portionsby the blade of the dicing saw.

With regard to the substrate 42 bonded substantially with 125 pieces ofthe thermoelectric material chips 45, the 125 pieces thereof weresubstantially related to PN junctions in view of their arrangement whenthe rectangular thermoelectric material wafer was used under thearrangement and the constitution of the thermoelectric material chipsprescribed in FIG. 3 and when the solder bumps were formed in 11 rows inthe longitudinal direction by 12 rows in the transverse direction (132pieces in total). In this case, with regard to unnecessary chips atouter peripheral portions, if any means of bonding was not provided,they were eliminated in the cutting and eliminating step resulting in noproblem. However, they might be preserved by bonding them to thesubstrate by any means since mechanical enforcement and electricreliability of the formed thermoelectric device could be promoted bypreserving the unnecessary chips by bonding them to the substrate. Inthis case, when enhancing of strength of the formed thermoelectricdevice was aimed, the thermoelectric device could be manufactured withno hindrance in steps if bonding pads for electrically isolated dummychips were previously formed on the substrate in forming the electrodesand bonded thereto as in the other bumps. Further, by bonding bumps ofthe unnecessary chips to the substrate in which pads wired toshortcircuit near electrodes were previously formed, it was possible topreserve the chips and to achieve the mechanical reinforcement and thepromotion of electric bonding reliability of the thermoelectric materialchips at the outermost peripheral portions.

In an integrating step (E), two sheet of the substrates 42 respectivelybonded with the thermoelectric material chips 45 of different types areopposed, the solder bumps formed on the distal ends of the respectivechips and the electrodes 43 formed on the substrate were positioned tolocations for bonding, the assembly was pressed and heated to melt thesolder whereby the thermoelectric material chips 45 and the electrodes43 on the substrate 46 were bonded thereby finishing the thermoelectricdevice having the PN junctions on the top and the bottom substrates.Further, positioning in bonding was performed by inserting the solderbumps 41 formed on the distal ends of the thermoelectric material chip45 of respective types into the inside of the doughnut-shaped structuresof the remaining larger ones (internal diameter; 140 μm, outer diameter;170 μm, height; 30 μm) among the structures 44 formed on the substrateof different types to be bonded. Larger ones of the doughnut-shapedstructures were selected in the positioning to facilitate thepositioning of the thermoelectric material chips and the electrodes ofthe substrate and to prevent the solder from oozing in this embodiment,whereby their effect as well as that of the smaller doughnut-shapedstructures in the bonding step (C) were sufficiently provided.

With respect to the final outer dimensions of the thermoelectric deviceformed as above, the thickness was approximately 1.2 mm (as for thecomponents of the thickness, the thickness of the thermoelectricmaterial chip was 0.5 mm, the thickness of the top and the bottomsubstrates respectively was 0.3 mm, the heights of the bonding materialand the nickel bump in sum at the top and the bottom bonding portionwere respectively 0.05 mm), the size was 4 mm×4 mm in the size of thelower substrate provided with input and output electrodes andelectrically the internal resistance was 120 Ω. The size of thethermoelectric device of this embodiment having the thermoelectricmaterial chips and the positional and arranging relationships of theelectrodes for PN bonding as shown by FIG. 3 and manufactured by themethod of making thereof, could not be achieved by the conventionalmanufacturing method in which the thermoelectric device was formed byforming the thermoelectric material chips and inserting them between thetop and the bottom substrates.

When lead wires were connected to input and output electrodes of thethermoelectric device and respective characteristics were investigated,the following results was provided.

With respect to the power generation function based on the Seebeckeffect, the open voltage between the substrates in a temperaturedifference of 2° C. was 90 mV and an output of 80 mV -70 μA was obtainedby attaching a load resistor of 1 KΩ to the outside when a temperaturedifference of 2° C. was provided between the substrates. Further, when16 pieces of the thermoelectric devices having 125 couples of PNjunctions were connected in series and was carried by enclosing them ina quartz oscillator type electronic wrist watch, the watch could bedriven at room temperature of 20° C.

With respect to the function of a cooling and heat generating elementbased on the Peltier effect, when an aluminium radiating plate wasadhered to the substrate on the heat generating side by a siliconeadhering agent having high thermal conductivity and a voltage of 6 V wasapplied between input electrodes, electric current of approximately 50mA flowed and a phenomenon was caused on the surface of the substrate onthe heat absorbing side in which moisture in the air was instantaneouslyfrozen by which it was proven that the function of the thermoelectricdevice as a Peltier device was very excellent.

EMBODIMENT-2

FIG. 5 is a perspective view viewing from a top substrate for explainingoutline of electrodes and thermoelectric material chips on a substrateof a thermoelectric device in accordance with EMBODIMENT-2. In FIG. 5,among lines showing electrodes, bold lines indicate an electrode pattern50 of a top substrate and dotted lines indicate electrode pattern 51 ofa bottom substrate. Incidentally, the expression of top substrate orbottom substrate is for convenience of explanation and naturally, anysubstrate may be a top or bottom one in the thermoelectric device.Further, quadrangles provided with two kinds of hatched linesrespectively indicate a P-type thermoelectric material chip 52 and aN-type thermoelectric material chip 53. Further, thermoelectric materialchips provided at the outer peripheral portions of the thermoelectricdevice that are not related to PN junctions (hereafter called dummychips), are bonded and fixed to the top substrate and the bottomsubstrate by dummy electrodes 54 of the top substrate and dummyelectrodes 55 of the bottom substrate. In FIG. 5, the dummy chip isconnected to the dummy electrode on one substrate and connected to theelectrode performing PN junction on the other substrate, however, theremay be dummy electrodes connected to both of the substrates. In eithercase, the dummy chips perform mechanical reinforcement of thethermoelectric device comprising small-scaled thermoelectric materialchips manufactured in this embodiment. As shown in FIG. 5, with regardto the arrangement of the thermoelectric material chips in thethermoelectric device of this embodiment, in viewing a certain row inthe X direction, only P-type thermoelectric material chips or onlyN-type thermoelectric material chips are arranged and the rows of theP-type thermoelectric material chips and the rows of the N-typethermoelectric material chips are alternately arranged. Meanwhile, inthe Y direction, in viewing a certain row, the P-type thermoelectricmaterial chips and the N-type thermoelectric material chips arealternately arranged.

In this embodiment, a thermoelectric device was manufactured having sucha structure and the arrangement of the thermoelectric material chips inwhich the size of the thermoelectric material chip in a section inparallel with the substrates was 500 μm, the height was 500 μm, thecenter distance between nearest thermoelectric material chips was 1,000μm and the number of the thermoelectric material chips (including dummychips) was 64 pieces in sum of the P-type and N-type ones.

As the thermoelectric material, a sintered body of Bi-Te series materialwhich was the same as that in EMBODIMENT-1 and of which function wasexcellent at around room temperature, was used. As major characteristicsof the thermoelectric material, in P-type, the Seebeck coefficient was205 μV/deg, the specific resistivity was 0.95 mΩ cm, the heatconductivity was 1.5 W/m·deg, and in N-type, the Seebeck coefficient was170 μV/deg, the specific resistivity was 0.75 mΩ cm and the heatconductivity was 1.5 W/m·deg. Alumina having the heat conductivity of 20W/m·deg was used as substrate material.

FIG. 6 is a view showing outline of steps for manufacturing thethermoelectric device. An explanation will be given to respective stepsin reference to FIG. 6 as follows.

In a bonding layer forming step (A), a nickel plating was performed onboth faces to be bonded to the substrate among surfaces of athermoelectric material wafer 60 having the thickness of 500 μm by a wetplating method by which a nickel layer 61 having the thickness of 10 μmwas formed. One of the faces on which the nickel layers were formed wasmasked, solder plating having the solder composition of tin:lead=1:9 wasperformed on the other face by a wet plating method by which a solderlayer 62 having the thickness of 30 μm was formed. Next, the platingmask was stripped, the solder layer 62 having the solder composition oftin:lead=1:9 was masked and a solder plating having the soldercomposition of tin:lead=6:4 was performed on another nickel layer 61 bya wet plating method by which a solder layer 63 having the thickness of30 μm was formed, and by stripping the plating mask a thermoelectricmaterial wafer having the solder layer 62 with the solder composition oftin:lead=1:9 on one face and the solder layer 63 with the soldercomposition of tin:lead=6:4 on the other face, was formed. Next, a rosingroup flux was coated on the solder layer 62 and 63 on the both facesand the solder was reflowed at 350° C. by which the solder layers weremade uniform and the surfaces thereof were cleaned. Incidentally, inregard of steps, the reflow treatment may be performed after a groovingstep that is successive to the bonding layer forming step.

In a grooving step (B), a dicing saw was used by which grooving wasperformed longitudinally and transversely on the side of the solderlayer 62 having the solder composition of tin:lead=1:9 up to the depthof 90 μm from the surface of the solder layer 62 by a blade having theblade width of 1.5 mm. The feed of the blade between grooves wasdetermined to be 2 mm such that an interval of a protrusion formedbetween the grooves became 0. 5 mm that was the size of thethermoelectric material chip. The depth of grooving was determined to be90 μm from the surface of the solder layer such that contiguousprotrusions were not shortcircuited in a later bonding step and thegrooves produced a gap between the thermoelectric material wafer and thesubstrate that was necessary in a later step of chip formation bycutting and eliminating.

In an electrode forming step (C), a copper plate having the thickness of0.1 mm on an alumina substrate 64 having the thickness of 0.5 mm havingthe thickness of 0.1 mm was worked into electrodes 65 by photoetchingconstituting the top substrate or the bottom substrate pattern as shownin FIG. 5.

In a bonding step (D), protrusions 68 of the thermoelectric wafer 60 andthe electrodes 65 were positioned and the solder layer 62 having thecomposition of tin:lead=1:9 of the protrusions was molten by which theelectrodes 60 and the thermoelectric wafer were bonded. The bondingtemperature at this instance was 340° C.

In a cutting and eliminating step (E), cutting and eliminating wereperformed by using a dicing saw with a blade having the blade width of1.5 mm with respect to cutting in the X direction specified in FIG. 5and with a blade having the blade width of 0.5 mm with respect tocutting in the Y direction without destructing the electrodes 65 on thesubstrate 64 in which blade edges were disposed at grooves (recess) 67formed in the grooving step thereby forming the thermoelectric materialchips 66.

In an integrating step (F), two sheets of the substrates 64 respectivelybonded with the thermoelectric material chips 66 of different types areopposed, the solder layer 63 having the solder composition oftin:lead=6:4 formed on the distal ends of the respective chips and theelectrodes 65 formed on the substrate 64 were positioned at locations atwhich the both were to be bonded, the assembly was heated while beingpressed to melt the solder whereby the thermoelectric material chips 66were bonded to the electrodes 65 on the substrate 64 by which thethermoelectric device having the PN junctions on the top and the bottomsubstrates could have been finished. Further, the temperature in bondingwas determined to be 230° C. at which the solder having the compositionof tin:lead=1:9 for the previous bonding was not molten. Accordingly,the integrating step could be performed without toppling or shifting thethermoelectric material chips even if structures were not providedaround the bonding portions.

The thermoelectric device of this embodiment was made by themanufacturing method essentially similar to that in making thethermoelectric device described in EMBODIMENT-1. Although the locationsand arrangement of the thermoelectric material chips and the arrangementof the electrodes for PN bonding in EMBODIMENT-1 are preferable when thethermoelectric material chips are extremely small, the locations andarrangement of the thermoelectric material chips and the arrangement ofthe electrodes for PN boding of this embodiment are preferable toenhance the density of the thermoelectric material chips in thethermoelectric device. Further, the thermoelectric device and the methodof making thereof according to this embodiment are preferable torestrict the amount of the thermoelectric material to be removed in thecutting and eliminating step.

With regard to the final outer dimensions of the thermoelectric deviceformed as above, the thickness was approximately 1.5 mm and the size was9 mm×8 mm in the size of the bottom substrate provided with input andoutput electrodes and electrically the internal resistance was 1 Ω. Itsfunction as a cooling and heat generating element based on the Peltiereffect was investigated by connecting lead wires to input electrodes ofthe thermoelectric device. When an aluminum radiating plate was adheredto the substrate on the heat generating side by a silicone adhesiveagent having high conductivity and when voltage of 1 V was appliedbetween the input electrodes, current of approximately 1 A flowed and arapid cooling was caused on the side of the heat absorbing substrate. Aratio of input power to an amount of heat absorbing, so called COP(coefficient of performance) was 0.55 at a temperature difference of 20°C. which proved that this thermoelectric device has excellent function.

EMBODIMENT-3

An explanation will be given of making a small-scaled thermoelectricdevice in which the size of thermoelectric material chips is 50 μm withrespect to a thermoelectric device having an electrode pattern similarto that in EMBODIMENT-1.

As the thermoelectric material, a sintered body of Bi-Te series materialwas used which was the same as that in EMBODIMENT-1 and was excellent inits function around room temperature. With regard to majorcharacteristics of the thermoelectric material, in P-type, the Seebeckcoefficient was 205 μV/deg, the specific resistivity was 0.95 mΩ cm andthe heat conductivity was 1.5 W/m·deg and in N-type, the Seebeckcoefficient was 170 μV/deg, the specific resistivity was 0.75 mΩ cm, andthe heat conductivity was 1.5 W/m·deg. As substrate material, a siliconwafer having the thickness of 300 μm which was electrically insulated bythermally oxidizing the surface was used. With regard to the size of thedevice and the like, the height of the thermoelectric chip was 500 μm,the shape of a thermoelectric material chip at a section in parallelwith the substrate was a square, the length of which side was 50 μm asabove, the center distance between nearest thermoelectric material chipsof a same kind in FIG. 3 was 100 μm (150 μm in center distance), thedistance between nearest thermoelectric material chips of differenttypes was 35 μm (150/√2=about 110 μm in center distance) and a number ofelement couples arranged in series in a single element was 51.

FIG. 7 is a view showing outline of steps for manufacturing thethermoelectric device of this embodiment. As shown in FIG. 7, themanufacturing method is grossly classified into five steps. Anexplanation will be given thereto in due order.

In a bump forming step (A), a photoresist having the thickness of 20 μmwas coated on the both faces of thermoelectric material wafers 70respectively of P-type and N-type having the thickness of 500 μm each ofwhich was made of a Bi-Te series sintered body. A pattern of the resistwas formed by exposing and developing the photoresist such that circularopenings each having the diameter of opening of 45 μm were formed andtheir arrangement was in a desired pattern. The desired pattern wasdetermined based on the above-mentioned dimensions such that the patternconformed to the arrangement of the thermoelectric material chips inFIG. 3. A nickel plating of 20 μm was firstly performed on the openingsto form so-called nickel bumps by an electric plating method aftercleaning them by an acid or the like. Next, a solder plating wasperformed on the nickel layer similarly by an electric plating method toform a solder layer of 30 μm. Here, the solder plating was performedsuch that the ratio of tin:lead became 6:4. Next, when a rosin groupflux was coated on the solder-plated layer after stripping thephotoresist and a reflow treatment was performed thereon at 230° C.,spherical solder bumps 71 having the diameter of approximately 50 μmcould be formed on the both faces of the thermoelectric material wafer70.

In an electrode forming step (B), films of chromium, nickel and goldrespectively having the thicknesses of 0.1 μm, 2 μm and 1 μm in thisorder from the side of the substrate were formed by a sputtering methodon the surface of a silicon wafer substrate 72 having the thickness of300 μm of which surface is provided with an oxide layer of 0.5 μm bythermal oxidation. Next, electrodes 73 were formed on the top and bottomsubstrates by photolithography such that they conformed to the electrodepatterns of FIG. 3. Further, two kinds of structures 74 each having abonding portion in a hollow cylindrical form around a portion of theelectrode to be bonded to the P-type thermoelectric material or theN-type thermoelectric material through the solder bumps were formed byphotolithography using a thick film photoresist. With regard to theshape and the size of the structures 74 constituted by the thick filmphotoresist, in one substrate among two sheets of substratesconstituting the thermoelectric device, the diameter of the cylinder ata location where the P-type thermoelectric material chip was disposedwas 60 μm, the diameter thereof at a location where the N-typethermoelectric material chip was disposed was 70 μm and the otherportions of the substrate was covered with the resist having thethickness of 40 μm. In the other substrate, the diameter at a locationwhere the P-type thermoelectric material chips was disposed was 70 μm,the diameter at a location where the N-type thermoelectric material chipwas disposed was 60 μm and the other portion of the substrate wascovered with the resist having the thickness of 40 μm. Here, thethickness of the resist was determined to be 40 μm to use the structuresformed thereby to produce a gap in a successive step (C) of bonding thethermoelectric material wafer 70 to the substrate 72 and a step (D)successive to step (C) of cutting and eliminating the thermoelectricmaterial wafer 70. In EMBODIMENT-1, the gap was produced by the nickelbumps. In EMBODIMENT-4, the gap between the thermoelectric materialwafer 70 and the substrate 72 necessary in the cutting and eliminatingstep (D) was 30 μm or more. By contrast, in forming the bumps 71 on thethermoelectric material wafer 70 in the preceding step, it was difficultto render the height of the nickel bumps producing the gap to be 20 μmor more due to a limitation of photolithography technology and platingtechnology.

In a bonding step (C), after performing a predetermined positioningbetween the thermoelectric material wafer 70 attached with the solderbumps 71 formed in the bump forming step (A) and the substrate 72 onwhich the electrodes 73 and the structures 74 in the vicinities of thebonding portions both were formed in the electrode forming step (B), thesolder was molten and the thermoelectric material wafer 70 was bonded tothe substrate 72. Further, in bonding the P-type thermoelectric materialwafer to the substrate, the positioning between the thermoelectricmaterial wafer 70 and the substrate 72 was performed by inserting thesolder bumps formed on the surface of the P-type thermoelectric materialwafer into the inside of openings for bonding of the structures 74having the diameter of 60 μm that were formed on the substrate.Similarly, in bonding the N-type thermoelectric material wafer to thesubstrate, the positioning between the thermoelectric material wafer 70and the substrate 73 was performed by inserting the solder bumps formedon the surface of the N-type thermoelectric material wafer into theinside of openings for bonding of the structure 74 having the diameterof 60 μm that were formed on the substrate. The smaller ones of theopenings for bonding of the two kinds of structures 74 that were formedon the substrate were used in bonding the thermoelectric material wafer70 to the substrate 72 to dispense with wrong bonding locations and topromote the mutual positioning accuracy.

In a cutting and eliminating step (D), the thermoelectric wafer 70bonded to the substrate 72 was transformed into thermoelectric materialchips 75 bonded to the substrate 72 by cutting and eliminating portionsof the thermoelectric material wafer. At this instance, portions of thesubstrate 72 might be cut and eliminated in accordance with thenecessity. In this embodiment, the cutting and eliminating step (D) wasperformed by using a dicing saw that was used in cutting siliconsemiconductors and the like. A blade having the thickness of 100 μm wasused in the cutting and eliminating step. The thickness of the blade wasselected under conditions in which the length of a side of a square ofthe thermoelectric material chip 70 in this embodiment was 50 μm, thecenter distance between nearest thermoelectric material chips of a samekind was 100 μm and the thermoelectric material chips of different kindswere bonded in the positional relationship in FIG. 3. The cutting andeliminating unnecessary portions of the thermoelectric material wasperformed at central portions between the solder bumps 71 and at thesame time by adjusting the height of the blade so as not to destruct theelectrodes 73 on the substrate by using a gap between the thermoelectricmaterial wafer 70 and the substrate 72 formed by the structures 74having the height of 40 μm. The substrate 72 substantially bonded with51 pieces of thermoelectric material chips 75 was manufactured withrespect to the thermoelectric materials of respective types bylongitudinally and transversely cutting and eliminating the portions bythe blade of the dicing saw.

Here, substantially 51 pieces of the thermoelectric material chips 75were bonded to the substrate 72, in which, in case where a rectangularthermoelectric material wafer was used in the arrangement and theconstitution of the thermoelectric material chips in FIG. 3 and thesolder bumps in 8 rows in the longitudinal direction by 7 columns thetransverse direction (56 pieces in sum) were formed, in regard of thearrangement, 51 pieces were substantially related to PN junctions. Inthis case, unnecessary portions of chips at outer peripheral portionswere removed by the cutting and eliminating step resulting in no problemif no bonding measure was performed. However, the unnecessary chipsmight be connected to the substrates and preserved since the mechanicalreinforcement and the electrical reliability could be promoted bybonding them to the substrate in preserving them. In this case, when theenhancement of the strength of the manufactured thermoelectric devicewas aimed, the thermoelectric device could be manufactured with nohindrance in steps if connecting pads for electrically isolated dummiesare previously provided on the substrate in making the electrodes andbonded thereto as in the other bumps. Further, by short circuiting thepads to near electrodes at which unnecessary chips are bonded to thesubstrate, the chips could be preserved and the mechanical reinforcementand the electrical bonding reliability of the thermoelectric materialchips at outermost peripheral portions could be promoted.

In an integrating step (E), two sheets of the substrates 72 respectivelybonded with the thermoelectric material chips 75 of different types wereopposed, the solder bumps 71 formed on the distal ends of the respectivechips and the electrodes 73 formed on the substrates were positioned tolocations to be bonded, the assembly was heated while being pressed tomelt the solder, whereby the thermoelectric material chips 75 and theelectrodes 73 of the substrate 72 were bonded by which thethermoelectric device having the PN junctions on the top and the bottomof the substrates could have been finished. Further, the positioning inbonding was performed by inserting the solder bumps 71 formed on thedistal ends of the thermoelectric material chips 75 of respective typesinto the inside of the remaining larger ones (70 μm in diameter) amongthe openings for bonding of the structures 74 formed on the substratesof different types to be bonded. The larger ones of the openings forbonding of the structures 74 were selected in positioning to facilitatethe positioning of the thermoelectric material chips and the substrateelectrodes and to prevent the solder from oozing and in this embodiment,the effect as well as that of the smaller openings for bonding of thestructure 74 in the bonding step (C) were sufficiently provided.

With respect to the final outer dimensions of the thermoelectric devicemanufactured as above, the thickness was approximately 1.2 mm, the sizewas 2 mm×2 mm in the size of the bottom substrate provided with inputand output electrodes and electrically the internal resistance was 180Ω. When lead wires were connected to the input and output electrodes ofthe thermoelectric device and respective properties were investigated,the following result was provided.

With regard to the power generating function based on the Seebeckeffect, the open voltage between the substrates in a temperaturedifference 2° C. was 35 mV and an output of 30 mV -30 μA was providedwhen a load resister of 1 KΩ was attached to the outside and atemperature of 2° C. was given between the substrate. Further, when 49pieces of the thermoelectric device having 51 couples of the PNjunctions were connected in series and the assembly was carried in awrist watch, the watch could be driven at room temperature of 20° C.

With respect to the function as a cooling and heat generating elementbased on the Peltier effect, an aluminum irradiating plate was adheredto the substrate on the heat generating side of the substrate by asilicone adhesive agent having high thermal conductivity and a voltageof 2V was applied between the input electrodes, current of approximately10 mA flowed and a phenomenon in which moisture in the air wasinstantaneously frozen on the surface of the substrate at the heatabsorbing side was caused by which it was proved that the function ofthe thermoelectric device as a Peltier device was very excellent.

EMBODIMENT-4

As explanation will be given of making a small-scaled thermoelectricdevice having structure in which the sectional shape of a thermoelectricmaterial chip is thick (70 μm) on the side of one substrate and thin (50μm) on the side of the other substrate in a thermal device havingstructure of electrodes as in EMBODIMENT-1.

As the thermoelectric material, a sintered body of Bi-Te series materialwas similarly used. As substrate material, a silicon wafer having thethickness of 300 μm that was electrically insulated by thermallyoxidizing its surface was used. With respect to the size of the elementand the like, the height of thermoelectric material chips was 500 μm,the shape of the thermoelectric material chip at sections in parallelwith the substrate was a square, the length of the side of the square ata section was 50 μm as mentioned above and that at a section proximateto one bonding portion was 70 μm. The center distance between nearestthermoelectric material chips of a same kind in FIG. 3 was 270 μm, thecenter distance between nearest thermoelectric material chips ofdifferent types was 270/√2=about 190 μm and a number of element couplesarranged in a single element in series was 51. (The calculation ofdistance was performed with the size of the chip as 70 μm).

FIG. 8 illustrates views showing outline of steps for manufacturing thethermoelectric device of EMBODIMENT-4. As shown in FIG. 3, themanufacturing method is grossly classified into 6 steps. An explanationwill be given thereto in due order.

In a bump forming step (A), a photoresist having the thickness of 101 μmwas coated on both faces of respective thermoelectric material wafers 40of P-type and N-type each comprising a Bi-Te series sintered body havingthe thickness of 500 μm. A resist layer having circular openings ofwhich diameter of opening was 40 μm on one face, of which diameter ofopening was 60 μm on the other face and the arrangement of which is in adesired pattern, was formed by exposing and developing the photoresist.Further, the desired pattern was determined based on the abovedimensions such that the pattern conformed to the arrangement of thethermoelectric material chips in FIG. 3. Next, a nickel plating of 10 μmwas performed firstly on the both faces of the openings by an electricplating method after cleaning them by an acid or the like by whichso-called nickel bumps were formed. Next, a solder plating was performedon the nickel layer similarly by an electric plating method to form asolder layer of 30 μm. The solder plating was performed such that aratio of tin to lead was 6:4. Next, when a rosin group flux was coatedon the solder plated layer after removing the photoresist and a reflowtreatment was performed at 230° C., spherical solder bumps 81 having thediameter of approximately 50 μm on one face and the diameter of 70 μm onthe other face could be formed on the both faces of the thermoelectricmaterial wafer 80.

In a grooving step (B), different grooving operations were performed onthe P-type thermoelectric material wafer and the N-type thermoelectricmaterial wafer. FIG. 9 illustrates views showing the width and the depthof the grooving in the grooving step of this embodiment. As shown inFIG. 9, firstly, grooving of the depth of 150 μm was longitudinally andtransversely performed at central portions between the solder bumps by adicing saw attached with a blade having the blade width of 160 μm onsurfaces on which the solder bumps having the diameter of 70 μm wereformed with respect to the P-type thermoelectric material wafer.Thereby, grooves having the width of 160 μm and the depth of 150 μmcould be formed and therefore, the P-type thermoelectric material waferin which the solder bumps having the diameter of approximately 70 μmwere formed on protrusions having the length of a side of 70 μm and theheight from the bottom of the groove of 150 μm could be formed. Groovingof the depth of 350 μm was performed longitudinally and transversely atcentral portions between the bumps by a dicing saw attached with a bladehaving the blade width of 180 μm on surfaces on which the solder bumpshaving the diameter of 50 μm were formed with respect to the N-typethermoelectric material wafer. Thereby, grooves having the width of 180μm and the depth of 350 μm could be formed and therefore, the N-typethermoelectric material wafer in which the solder bumps having thediameter of approximately 50 μm were formed on protrusions having thelength of a side of 50 μm and the depth from the bottom of the groove of350 μm could be formed. The reason of the grooving formed in such a waywas that in addition to forming a gap between the thermoelectricmaterial wafer and the substrate that is necessary in a bonding step (D)and in a cutting and eliminating step (E) in FIG. 8 that are latersteps, by changing the sectional shape of the thermoelectric materialchip in direction orthogonal to the substrates, in case where themanufactured thermoelectric device was used as a Peltier element, Jouleheat by flowing current was to be generated as much as possible on theside of a heat radiating substrate and heat flow to the side of a heatabsorbing substrate was to be prevented.

In an electrode forming step (C) in FIG. 8, films of chromium, nickeland gold in this order from the substrate respectively having thethicknesses of 0.1 μm, 1 μm and 0.1 μm were formed by a sputteringmethod on the surface of a silicon wafer substrate 82 having thethickness of 300 μm and provided with an oxide layer of 0.5 μm on itssurface by thermal oxidation. Next, electrodes 83 were formed to conformto the electrode pattern specified in FIG. 3. On one of the substrate,doughnut-shaped structures 84 having the internal diameter of 80 μm, theouter diameter of 110 μm and the height of 30 μm were formed byphotolithography using a cured thick film photoresist at thesurroundings of portions to be bonded by the solder bumps. On the otherones of the substrates, doughnut-shaped structures 84 having theinternal diameter of 60 μm, the outer diameter of 90 μm and the heightof 30 μm were formed by photolithography using a thick film photoresistat the surroundings of portions to be bonded by the solder bumps.

In a bonding step (D) in FIG. 8, the thermoelectric material wafer 80attached with the solder bumps 81 formed by the bump forming step (A)and the substrate 82 formed with the electrodes 83 and thedoughnut-shaped structure 84 in the vicinity of the bonding portionswhich had been made in the electrode forming step (C) were positioned atpredetermined locations and thereafter, the solder was molten by whichthe thermoelectric material wafer 80 and the substrate 82 were bonded.In the bonding, the solder bumps on the surface of the thermoelectricmaterial wafer 80 on which the grooving had been performed and thedoughnut-shaped structures 84 on the substrate 82 were positioned atpredetermined locations and heating and bonding were performed whilepressing the substrate 82 from outside. The P-type thermoelectricmaterial wafer was bonded to the substrate in which the structureshaving the internal diameter of 80 μm, the outer diameter of 110 μm andthe height of 30 μm were formed by the solder bumps having the diameterof 70 μm which had been formed on the surface on which the grooving hadbeen performed and the N-type thermoelectric material wafer was bondedto the substrate on which the structures having the inner diameter of 60μm, the outer diameter of 90 μm and the height of 30 μm were formed bythe solder bumps having the diameter of 50 μm formed on the surface onwhich the grooving had been performed.

In a cutting and eliminating step (E) the thermoelectric material wafer80 bonded to the substrate 82 was formed into thermoelectric materialchips 85 bonded to the substrate 82 by cutting and eliminating portionsof the thermoelectric material wafer. At this instance, portions of thesubstrate 82 might simultaneously be cut and eliminated in accordancewith the necessity. As in EMBODIMENT-1, also in this embodiment, thecutting and eliminating step (E) was performed by using a dicing sawthat was used in cutting silicon semiconductors and the like. Withrespect to a blade used in the cutting and eliminating step, a bladehaving the blade thickness of 180 μm was used in cutting and eliminatingportions of the P-type thermoelectric material wafer and a blade havingthe blade thickness of 160 μm was used in cutting and eliminatingportions of the N-type thermoelectric material wafer. In the P-typethermoelectric material wafer, the grooves having the width of 160 μmhad been cut by 150 μm from the side of the substrate in the groovingstep and therefore, in the cutting and eliminating step (E), the cuttingand eliminating was performed by a blade having the blade thickness of180 μm and up to the depth of 350 μm from the surface of the remainingportion of the thermoelectric material wafer on the opposite sidethereof wherein the grooves having the width of 160 μm and the depth of150 μm had been cut. In the N-type thermoelectric material wafer, thegrooves having the width of 180 μm had already been cut by 350 μm fromthe side of the substrate in the grooving step and therefore, in thecutting and eliminating step (E), the cutting and eliminating wasperformed by the blade of 160 μm from the surface of the remainingportion of thermoelectric material wafer having the thickness of 150 μmon the opposite side hereof wherein the grooves having the width of 180μm and the depth of 350 μm had been cut. FIG. 10 illustrates sectionalviews of the substrates to which the thermoelectric material chips madeby this operation had been bonded in a direction orthogonal to thesubstrates. As shown in FIG. 10, in the P-type thermoelectric materialchip, the size of a side is 70 μm up to 150 μm from the substrate andthe size is 50 μm for the remaining portion of 150 μm to 500 μmtherefrom and in the N-type thermoelectric material chip, the size is 50μm up to 350 μm from the substrate and the size is 70 μm for theremaining portion of 350 μm to 500 μm therefrom.

In an integrating step (F) in FIG. 8, two sheets of the substrates 82respectively bonded with the thermoelectric material chips 85 ofdifferent types were opposed, the solder bumps 81 formed on the distalends of the respective chips and the electrodes 83 formed on thesubstrates were positioned at locations to be bonded and the assemblywas heated while being pressed to melt the solder whereby thethermoelectric material chips 85 were bonded to the electrodes 83 on thesubstrates 82 by which the thermoelectric device having the PN junctionson the top and the bottom substrates could have been finished. Further,the positioning in this bonding was performed by the structures 84formed on the substrates of different types to be bonded to the solderbumps 81 which had been formed on the distal ends of the thermoelectricmaterial chips 85 of respective types.

FIG. 11 is a view indicating outline of the thermoelectric device madeby the series of step. Although the constitution of the device issimilar to the device manufactured in EMBODIMENT-1, the sectional shapesof the P-type thermoelectric material chip 110 and the N-typethermoelectric material chip 111 are not in a single rectangular formand those in both of the P-type and the N-type are thick on the side ofone substrate 116 and thin on the side of the other substrate 113.

To investigate the function of the thermoelectric device ofEMBODIMENT-4, thermoelectric devices respectively having sizes ofthermoelectric material chips of 50 μm and 70 μm and having the samenumber of PN junctions and the outer dimensions were manufactured andthe function as a Peltier element was compared among the three devices.Then, the device of this embodiment indicated a value of the COP(coefficient of Performance) superior to those of the respectivecomparison samples by approximately 10% showing the most excellentfunction.

In a Peltier device, Joule heat is generated by flowing current inaddition to heat generation on the side of a radiating substrate causedby the transfer of heat by the Peltier effect. As is well known, in theJoule heat generation, in case where the section of a substance in whichcurrent flows is uniform, a central portion thereof is mostly heated andgenerates heat. In the thermoelectric device of this embodiment, bymaking current flow such that the substrate having the thinnerthermoelectric material chips became a heat radiating substrate, theJoule heat generation was caused centering on the portions in which thethermoelectric material chips are thinned. Therefore, the generated heatwas smoothly transferred from a nearer substrate, that is, the heatradiating substrate and accordingly, heat could be prevented fromflowing to a heat absorbing substrate on the opposite side by which thethermoelectric device was provided with high function.

Further, although the sectional view showing of the outline of thethermoelectric device in EMBODIMENT-4 is illustrated in FIG. 11,considering the easiness of manufacturing a thermoelectric device,especially the positioning or the bonding of the thermoelectric materialchips to the substrate in the integrating step, a sectional shape shownin FIG. 12 is also effective.

EMBODIMENT-5

An explanation will given of an embodiment of manufacturing asmall-scaled thermoelectric device in which thermoelectric material andsubstrates are bonded by a method other than the solder bump method in athermoelectric device having an electrode pattern similar to that inEMBODIMENT-1. The size of thermoelectric material chips, a number ofcouples of PN junctions, used material and the like are the same asthose in EMBODIMENT-1.

FIG. 13 illustrates views showing outline of steps for manufacturing athermoelectric device of this embodiment. As shown in FIG. 13, themanufacturing method is grossly classified into five steps. Anexplanation will be given thereto in due order.

In a protruded electrode forming step (A), a photoresist having thethickness of 50 μm was coated on both faces of respective thermoelectricmaterial wafers 130 of P-type and N-type each comprising a Bi-Te seriessintered body having the thickness of 500 μm. A resist layer havingcircular openings of which diameter of opening was 90 μm and thearrangement of which was in a desired pattern was formed by exposing anddeveloping the photoresist. The desired pattern was determined based onthe above-mentioned dimensions such that it became the arrangement ofthermoelectric material chips specified in FIG. 3. Next, a nickelplating of 50 μm was performed on the openings by an electric platingmethod after cleaning them with an acid or the like thereby forming aprotruded nickel layer. Next, a gold plating was performed on the nickellayer similarly by an electric plating method thereby forming a goldlayer of 1 μm. Next, the protruded electrodes 131 comprising nickel-goldwas formed by removing the resist. Here, the gold layer was provided toprevent the surface of nickel from being oxidized and to facilitatesoldering in a later step and therefore, the gold layer was not alwaysnecessary if there was no concern of oxidation.

In an electrode forming step (B), films of chromium, nickel and gold inthis order from the side of a substrate respectively having thethicknesses of 0.1 μm, 3 μm and 1 μm were formed by a sputtering methodon a silicon wafer substrate 132 having the thickness of 300 μm on thesurface of which an oxide layer of 0.5 μm had been provided by thermaloxidation. Next, electrodes 133 were formed on each of top and bottomsubstrates by photolithography to form the electrode pattern specifiedin FIG. 3 and a solder paste was printed on the electrodes 133 therebyfinishing the electrode wirings 133.

In a bonding step (C), the thermoelectric material wafer 130 having theprotruded electrodes 131 formed in the protruded electrode forming step(A) and the substrate 132 on which the electrodes 133 had been formed inthe electrode forming step (B), were positioned at predeterminedlocations and solder was molten whereby the thermoelectric materialwafer 130 and the substrate 132 were bonded. (Incidentally, the termstop or bottom have been provided for convenience of expression only asmentioned above and there is no top or bottom in the substrates of thisthermoelectric device).

In a cutting and eliminating step (D), the thermoelectric material wafer130 bonded to the substrate 132 was formed into thermoelectric materialchips 134 bonded to the substrate 132 by cutting and eliminatingportions of the thermoelectric material wafer 130. At this instance,portions of the substrate 132 might simultaneously be cut and eliminatedin accordance with the necessity. In this embodiment, the cutting andeliminating step (D) was performed by using a dicing saw used in cuttingsilicon semiconductors and the like. A blade used in the cutting andeliminating had the thickness of 200 μm. The thickness of the blade wasselected under conditions in which the length of a side of the squarethermoelectric material chip 134 in this embodiment was 100 μm, thecenter distance of nearest thermoelectric material chips of a same typewas 300 μm and the thermoelectric material chips of different types werebonded conforming to the positional relationships specified in FIG. 3.Unnecessary portions of the thermoelectric material were cut andeliminated at central portions between the protruded electrodes 131 andthe height of the blade was adjusted by using a gap between thethermoelectric material wafer 130 and the substrate 132 produced by theprotruded electrodes 131 having the height of 50 μm so as not todestruct the electrodes 133 on the substrate. The substrate 132substantially bonded with 125 pieces of the thermoelectric materialchips 134 was made for respective type of the thermoelectric material bylongitudinally and transversely cutting and eliminating using the bladeof a dicing saw.

In an integrating step (E), two sheets of the substrates 132respectively bonded with the thermoelectric material chips 134 ofdifferent types were opposed and the protruded electrodes 131respectively formed on the distal ends of the chips and the electrodes133 formed on the substrates and comprising solder layers werepositioned at locations to be bonded and the assembly was heated whilebeing pressed to melt the solder whereby the thermoelectric materialchips 134 and the electrodes 133 on the substrates 132 were bonded bywhich the thermoelectric device having PN junctions on the top and thebottom substrates could have been finished.

With respect to the final outer dimensions of the thermoelectric devicemanufactured as above, the thickness was approximately 1.2 mm, the sizewas 4 mm×4 mm in the size of the bottom substrate having input andoutput electrodes, electrically the internal resistance was 120 Ω andthe basic characteristics thereof were the same as those in thethermoelectric device manufactured in EMBODIMENT-1.

EMBODIMENT-6

An explanation will be given of an embodiment of manufacturing asmall-scaled thermoelectric device in which thermoelectric material andsubstrates are bonded by the solder bump method and a method using anelectrically conductive adhesive agent in a thermoelectric device havingan electrode pattern similar to that in EMBODIMENT-1. The size of athermoelectric material chip, a number of couples of PN junctions, usedmaterial and the like are the same as those in EMBODIMENT-1.

FIG. 14 illustrates views showing outline of steps in manufacturing athermoelectric device of this embodiment. As shown in FIG. 14, themanufacturing method is grossly classified into five steps. Anexplanation will be given thereto in due order.

In a bump forming step (A), a photoresist having the thickness of 50 μmwas coated on one face of each of thermoelectric material wafers 140 ofP-type and N-type comprising a Bi-Te series sintered body having thethickness of 500 μm. A resist layer having circular openings of whichdiameter of opening was 90 μm and the arrangement of which was in adesired pattern was formed by exposing and developing the photoresist.The desired pattern was determined based on the above dimensions toconform to the arrangement of thermoelectric material chips specified inFIG. 3. A plating resist was coated on the other face not coated withthe photoresist. Next, firstly, a nickel plating of 40 μm was coated onthe openings by an electric plating method after cleaning them by anacid or the like to form so-called nickel bumps. Next, a solder platingwas performed on the nickel layer similarly by an electric platingmethod to form a solder layer of 30 μm. In the solder plating, a ratioof tin to lead was 6:4. Next, after removing the photoresist and theplating resist, a rosin group flux was coated on the solder-plated layerand a reflow treatment was performed at 230° C. whereby spherical solderbumps 141 having the diameter of approximately 100 μm were formed on theone face of the thermoelectric material wafer 140.

In an electrode forming step (B), films of chromium, nickel and gold inthis order from the side of a substrate respectively having thethicknesses of 0.1 μm, 3 μm and 1 μm were formed on the surface of asilicon wafer substrate 142 having the thickness of 300 μm the surfaceof which was provided with an oxide layer of 0.5 μm by thermaloxidation. Next, electrodes 143 were formed on the top and the bottomsubstrates by photolithography to form the same electrode pattern as inFIG. 3. Further, two kinds of doughnut-shaped structures 144 were formedat the surroundings of portions to which a P-type thermoelectricmaterial and a N-type thermoelectric material were to be bonded throughsolder bumps by photolithography using a polyamide group photoresist.The structures 144 comprising the polyamide group photoresist wereprovided with a doughnut shape having the internal diameter of 120 μm,the outer diameter of 150 μm and the height of 30 μm at locations towhich the P-type thermoelectric material chips were disposed and theinternal diameter of 150 μm, the outer diameter of 170 μm and the heightof 30 μm at locations to which the N-type thermoelectric material chipswere disposed in one of two sheets of the substrates constituting thethermoelectric conversion element and in the other substrate, they wereprovided with a doughnut shape having the inner diameter of 150 μm, theouter diameter of 170 μm and the height of 30 μm at locations to whichthe P-type thermoelectric material chips were disposed and the internaldiameter of 120 μm, the outer diameter of 150 μm and the height of 30 μmat locations to which the N-type thermoelectric material chips weredisposed.

In a bonding step (C) the thermoelectric material wafer 140 and thesubstrate 142 in which the electrodes 143 and the doughnut-shapedstructures in the vicinities of bonding portions formed in the electrodeforming step (B) were opposed at predetermined locations and the solderwas molten whereby the thermoelectric material wafer 140 and thesubstrate 142 were bonded. Further, in bonding the P-type thermoelectricmaterial wafer and the substrate, the positioning of the thermoelectricmaterial wafer 140 and the substrate 142 was performed by inserting thesolder bumps formed on the surface of the P-type thermoelectric materialwafer into the inside of the smaller doughnut-shaped structures 144having the inner diameter of 120 μm, the outer diameter of 150 μm andthe height of 30 μm formed on the substrate. Similarly, in bonding theN-type thermoelectric material wafer and the substrate, the positioningof the thermoelectric wafer 140 and the substrate 142 was performed byinserting the solder bumps formed on the surface of the N-typethermoelectric material wafer into the inside of the smallerdoughnut-shaped structures 144 having the inner diameter of 120 μm, theouter diameter of 150 μm and the height of 30 μm formed on thesubstrate. Here, the smaller structures among the doughnut-shapedstructures having two sizes formed on the substrate were used in bondingthe thermoelectric material wafer 140 and the substrate 142 to dispensewith wrong bonding locations and to enhance mutual positioning accuracy.

In a cutting and eliminating step (D), the thermoelectric material wafer140 bonded to the substrate 142 were formed into thermoelectric materialchips 145 bonded to the substrate 142 by cutting and eliminatingportions of the thermoelectric material wafer. At this instance,portions of the substrate 142 might simultaneously be cut and eliminatedin accordance with the necessity. In this embodiment, the cutting andeliminating step (D) was performed by using a dicing saw used in cuttingsilicon semiconductors and the like. A blade used in the cutting andeliminating step had the thickness of 200 μm. The thickness of the bladewas selected under conditions in which the length of a side of thesquare thermoelectric material chip 145 of this embodiment was 100 μm,the center distance between nearest thermoelectric material chips of asame kind was 300 μm and the thermoelectric material chips of differentkinds were bonded in the positional relationship specified in FIG. 3.Unnecessary portions of the thermoelectric material were cut andeliminated at central portions between the solder bumps 141 and at thesame time the height of the blade was adjusted by utilizing a gapbetween the thermoelectric material wafer 140 and the substrate 142produced by the nickel bumps having the height of 40 μm so as not todestruct the electrodes 143 on the substrate. The substrate 142substantially bonded with 125 pieces of the thermoelectric materialchips 145 was made for each type of the thermoelectric materials bylongitudinally and transversely cutting and eliminating thereof by theblade of a dicing saw.

In an integrating step (E), an electrically conductive adhesive agenthaving silver particles and epoxy resin as major components was madeadhere to distal ends of the thermoelectric material chips 14 bystamping in two sheets of the substrates respectively bonded with thethermoelectric material chips 145 of different types, they were opposed,the distal ends of the thermoelectric material chips 145 and theelectrodes 143 formed on the substrates 142 were positioned at locationsto be bonded and the assembly was heated while being pressed whereby theelectrically conductive adhesive agent was cured and the thermoelectricmaterial chips 145 and the electrodes 143 on the substrates 142 werebonded by which the thermoelectric device having PN junctions on the topand the bottom substrates could have been finished. Further, the bondingwas performed at the insides of the remaining doughnut-shaped structures144 and the electrically conductive adhesive agent could be preventedfrom oozing in bonding by using the doughnut-shaped structures 144.

With regard to the final outer dimensions of the thermoelectric devicemanufactured as above, the thickness was approximately 1.2 mm, the sizewas 4 mm×4 mm in the size of the bottom substrate having input andoutput electrodes, electrically the internal resistance was 120 Ω andits basic characteristics were the same as those in the thermoelectricdevice manufactured in EMBODIMENT-1.

In this embodiment, in the step of forming the bumps on thethermoelectric material, the plating resist was not formed on the bothfaces by photolithography and therefore, there was no need of coating aphotoresist on the both faces and using both a face aligner and anexposure device which could simplify apparatuses and steps.

As stated above, although the explanation has been given to the presentinvention with respect to the embodiments, the present invention is notrestricted to the above embodiments and a broad application isconceivable. For example, although the sintered body of a Bi-Te seriesthermoelectric material was used in the respective embodiments asthermoelectric material, the present invention is naturally notrestricted to this thermoelectric material and various thermoelectricmaterials of Fe-Si series material, Si-Ge series material, Co-Sb seriesmaterial and the like are applicable. Further, although the descriptionhas been given to small-scaled thermoelectric devices and their methodsof making in the respective embodiments, according to the thermoelectricdevice and the method of making thereof of the present invention, thepresent invention is also applicable to a comparatively largethermoelectric device which is manufactured by the conventional methodin which thermoelectric material chips are interposed by two sheets ofsubstrates after they have been formed.

EMBODIMENT-7

The present invention will now be described on the basis of oneembodiment thereof and with reference to the accompanying drawings.

FIG. 15 is a view showing only a metal wiring part of a thermoelectricdevice produced by sandwiching between two alumina substrates a PNjunction comprising a P-type thermoelectric material and an N-typetermoelectric material connected through a metal, with the view beingtaken from above one of the substrates.

In FIG. 15, solid line parts 1 show an electrode pattern for the PNjunctions provided on the top substrate and dashed lines 152 showelectrode patterns for the PN junction provided on the bottom substrate.The P-type thermoelectric materials chips 153 and the N-typethermoelectric materials chips 154 mutually disposed at the parts wherethese continuous lines and dashed lines cross and are linked in seriesbetween two input/output electrodes 155 (hereinafter, between twoelectrodes will be refered to as between electrodes). Electrodes 156 areprovided at the outer periphery of the wiring on the bottom substrate asdevice repair and inspection electrodes for the present invention. Theexistence of defects such as disconnections existing between theelectrodes 156 (for example, between the electrodes 156-a and 156-b inFIG. 15) can be investigated by providing a number of electrodes 156 andby connecting with inspection probe electrodes between the electrodes.Also, if a defect exists between the electrodes 156, the defective partcan be electrically isolated by making electrical connections betweenthe electrodes and a device can be formed just using non-defectiveparts. For example, if there is a disconnection at the point A in FIG.15, the device can be made to function by electrically making ashort-circuit between the electrode 156-a and the electrode 156-b.

In FIG. 15, several tens thermoelectric material chips are sandwichedbetween the substrates but this diagram is for simplifying theexplanation. The inventor carried out experiments for a heat differencepower generating comprised of 50 rows in the X-direction of FIG. 15 and10 rows in the Y-direction so that a disconnection at one place resultsin the elimination of tow rows (10 pairs of elements) in theX-direction, and the reduction of the power-generating performance isproportional to the ratio of the number of elements eliminated.Reductions in performance change depending on the purpose of the butwith devices where the object is temperature difference power generationor refrigeration where the number of elements has been made large areduction in the number of elements of a few to 10% is not a problem.However, this problem can be resolved by anticipating the number ofdefective elements beforehand and increasing the number of elements bythis portion. In the case of a device having the kind of wiringstructure in FIG. 15, the ratio of the number of elements which do notoperate with respect to the overall number of elements upon theoccurrence of defects such as discontinuities, can be made small, byadopting a wiring structure where the number of elements in the Ydirection in the drawing is reduced to as great an extent as possibleand the number of elements in the X direction is increased.

As explained above, according to the inventions described inembodiments, a thermoelectric material wafer and PN bonding electrodeson a substrate are bonded under a positional relationship ofthermoelectric material chips and the PN bonding electrodes, thethermoelectric material chips bonded to the substrate are formed bycutting and eliminating unnecessary portions of thermoelectric material,the substrates respectively bonded with the thermoelectric materialchips of different types are opposed and PN junctions are formed bybonding distal ends of the thermoelectric material chips and the PNbonding electrodes on the substrate. Therefore, there is an effectcapable of manufacturing a thermoelectric device in which the size ofthe thermoelectric material chip is small and the density of a number ofthe thermoelectric material chips per unit area is high.

Further, according to the present inventions, by forming electrodes aswiring on a substrate of a thermoelectric device, inspection of thethermoelectric device can be carried out and it is possible toinvestigate defects such as disconnections or defective connections.Further, when defects exist, the functioning of a thermoelectric devicecan still be exhibited by connecting electrodes so as to exclude thedefective portion. As a result of this, the device construction yieldrate is markedly increased and costs are reduced.

Further, each thermoelectric device manufactured as above which is smalland thin and is provided with a number of couples of PN junctions of thethermoelectric material chips, achieves a considerable effect in powergenerating in a small temperature difference. In EMBODIMENT-1, anexample has been shown in which an electronic wrist watch was driven byusing the thermoelectric devices each having couples of PN junctions ofa number capable of outputting approximately 1 V or more. However, thenumber of devices can considerable be decreased when a step-up circuitis attached thereto or CMOS-ICs are driven at a low voltage andtherefore, the thermoelectric device is applicable not only to theelectronic wrist watch but to many carrying electronic instruments.Further, in using the small-scaled thermoelectric device manufactured bythe present invention as a cooling device an enormous effect isprovided.

For example, when the current density per thermoelectric material chipis made constant to equalize cooling function, the cooling capacity canbe enhanced by increasing the voltage since the sectional area of thethermoelectric material chip can be small and many thermoelectricmaterial chips can be arranged in series. For example, the coolingfunction is determined by power inputted to a thermoelectric device andin a conventional thermoelectric device, power supply causes low voltageand high current since the sectional area of a thermoelectric materialchip is large. By contrast, with regard to the thermoelectric device ofthe present invention, power can be supplied at low current since thesectional area of the thermoelectric material chips can be reduced.Thereby, it is not necessary to make thick wirings for inputting andoutputting and to provide a large current-type power source for use.Further, a multi-stage element called a cascade type can easily bemanufactured since electric wirings can be made thin by which anextremely low temperature can be achieved.

Further, although the size of the thermoelectric material chip was 500μm or less in the embodiments, with respect to the size, the presentinvention is naturally applicable to the size of several hundred μm tomm order that is a general size. Although the description has been givenof making individual thermoelectric devices in the embodiments, it ispossible to manufacture a plurality of devices in one operation by usinglarge-scaled substrates and thermoelectric material wafers. Therefore,the present invention achieves an enormous effect in manufacturingsmall-scaled thermoelectric devices in view of the production cost.

What is claimed is:
 1. A method of making a thermoelectric device,comprising the steps of: forming electrodes on each of two sheets ofsubstrates; bonding a P-type thermoelectric material plate to one of thesubstrates; bonding an N-type thermoelectric material plate to the otherof the substrates; cutting and eliminating portions of each bondedthermoelectric material plate to form separate substrates bonded withP-type and N-type thermoelectric material chips, respectively; andintegrating the thermoelectric device by opposing the substrate bondedwith the P-type thermoelectric material chips to the substrate bondedwith the N-type thermoelectric material chips and bonding the electrodesformed on the substrates to distal ends of the thermoelectric materialchips to thereby form pairs of PN-junctions.
 2. A method of making athermoelectric device according to claim 1; wherein a gap is formedbetween each of the substrates and a respective one of thethermoelectric material plates during the step of bonding thethermoelectric material plates to the substrates.
 3. A method of makinga thermoelectric device according to claim 1; including the step offorming bumps having a preselected shape and arrangement pattern andmade of at least one of the materials selected from the group consistingof solder, gold, silver, copper and nickel on at least one surface ofeach of the thermoelectric material plates; and wherein the step ofbonding the thermoelectric material plates to the substrates comprisesbonding the thermoelectric material plates to the substrates through thebumps.
 4. A method of making a thermoelectric device according to claim1; wherein a gap is formed between each of the substrates and arespective one of the thermoelectric material plates during the step ofbonding the thermoelectric material plates to the substrates by bumpsformed on a surface of each of the thermoelectric material plates.
 5. Amethod of making a thermoelectric device according to claim 1; wherein agap is formed between each of the substrates and a respective one of thethermoelectric material plates during the step of bonding thethermoelectric material plates to the substrates by structures formed onthe substrates.
 6. A method of making a thermoelectric device accordingto claim 1; further comprising a step of forming bumps on a surface ofeach of the thermoelectric material plates other than the surface ofeach of the thermoelectric material plates bonded to the substratesafter the step of bonding the thermoelectric material plates to thesubstrates.
 7. A method of making a thermoelectric device according toclaim 1; further comprising a step of processing the entire surface orportions of the surface of each of the thermoelectric material platesbefore bonding the thermoelectric material plates to the substrates toform protruding bonding portions for bonding the thermoelectric materialplates to the substrates.
 8. A method of making a thermoelectric deviceaccording to claim 1; further comprising a step of processing the entiresurface or portions of the surface of each of the thermoelectricmaterial plates before bonding the thermoelectric material plates to thesubstrates to form grooves for bonding the thermoelectric materialplates to the substrates.
 9. A method of making a thermoelectric deviceaccording to claim 1; further comprising a step of forming protrudingportions by grooving the entire surface or portions of the surface ofeach of the thermoelectric material plates on which a bonding materiallayer is formed before the step of bonding the thermoelectric materialplates to the substrates.
 10. A method of making a thermoelectric deviceaccording to claim 1; further comprising the steps of forming bumps onthe surface of each of the thermoelectric material plates and grooving aportion of the surface of the thermoelectric plates between the bumpsbefore bonding the thermoelectric material plates to the substrates. 11.A method of making a thermoelectric device according to claim 1; furthercomprising a step of forming grooves having a first preselected width onat least one of the surfaces of each of the thermoelectric materialplates before the step of bonding the thermoelectric material plates tothe substrates; and wherein the cutting and eliminating step comprisescutting the portions of the thermoelectric material plates with a secondpreselected cutting width different from the first cutting width.
 12. Amethod of making a thermoelectric device, comprising the stepsof:bonding a P-type thermoelectric material plate to a first substratehaving electrodes; bonding an N-type thermoelectric material plate to asecond substrate having electrodes; cutting and removing portions ofeach of the thermoelectric material plates to form P-type and N-typethermoelectric material chips bonded to the first and second substrates,respectively; and bonding the N-type thermoelectric material chips ofthe second substrate to the electrodes of the first substrate andbonding the P-type thermoelectric material chips of the first substrateto the electrodes of the second substrate to form PN-junctions betweenthe first and second substrates.
 13. A method of making a thermoelectricdevice according to claim 12; wherein a gap is formed between the P-typethermoelectric material plate and the first substrate and between theN-type thermoelectric material plate and the second substrate when theP-type thermoelectric material plate and the N-type thermoelectricmaterial plate are bonded to the first and second substrates,respectively.
 14. A method of making a thermoelectric device accordingto claim 12; including the step of forming bumps having a preselectedsize and arrangement pattern on at least one surface of each of thethermoelectric material plates before bonding the thermoelectricmaterial plates to the substrates.
 15. A method of making athermoelectric device according to claim 14; wherein the bumps arecomprised of a material selected from the group consisting of solder,gold, silver, copper and nickel.
 16. A method of making a thermoelectricdevice according to claim 14; including the step of forming connectingelements on a surface of each of the substrates before bonding thethermoelectric material plates to the substrates; and wherein the stepof bonding the thermoelectric material plates to the substrates includesconnecting each of the bumps of the thermoelectric material plates toone of the connecting elements of the substrates to position thethermoelectric material plates on the substrates with a gaptherebetween.
 17. A method of making a thermoelectric device accordingto claim 14; including the step of grooving a portion of the surface ofeach of the thermoelectric material plates between the bumps beforebonding the thermoelectric material plates to the substrates.
 18. Amethod of making a thermoelectric device according to claim 12;including the step of forming grooves on at least one surface of each ofthe thermoelectric material plates before bonding the thermoelectricmaterial plates to the substrates.
 19. A method of making athermoelectric device, comprising the steps of:forming electrodes on asurface of a first substrate and on a surface of a second substrate;disposing a P-type thermoelectric material plate and an N-typethermoelectric material plate on the surfaces of the first and secondsubstrates, respectively; processing the P-type thermoelectric materialplate and the N-type thermoelectric material plate to form P-typethermoelectric material chips and N-type thermoelectric material chips,respectively; disposing the first substrate over the second substrate sothat the P-type thermoelectric material chips face the N-typethermoelectric material chips; and connecting the P-type thermoelectricmaterial chips to the electrodes of the second substrate and connectingthe N-type thermoelectric material chips to the electrodes of the firstsubstrate to form PN-junctions between the first and second substrates.20. A method of making a thermoelectric device according to claim 19;wherein the processing step comprises cutting and removing portions ofthe thermoelectric material plates.
 21. A method of making athermoelectric device according to claim 19; including the step offorming bumps having a preselected size and arrangement pattern on atleast one surface of each of the thermoelectric material plates beforedisposing the thermoelectric material plates on the substrates.
 22. Amethod of making a thermoelectric device according to claim 21; whereinthe bumps are comprised of a material selected from the group consistingof solder, gold, silver, copper and nickel.
 23. A method of making athermoelectric device according to claim 21; including the step offorming connecting elements on the surface of each of the substratesbefore disposing the thermoelectric material plates on the substrates;and wherein the step of disposing the thermoelectric material plates onthe substrates comprises bonding each of the bumps of the thermoelectricmaterial plates to one of the connecting elements of the substrates toposition the thermoelectric material plates on the substrates with a gaptherebetween.
 24. A method of making a thermoelectric device accordingto claim 21; including the step of grooving a portion of the surface ofeach of the thermoelectric material plates between the bumps beforedisposing the thermoelectric material plates on the substrates.
 25. Amethod of making a thermoelectric device according to claim 19;including the step of forming grooves on at least one surface of each ofthe thermoelectric material plates before disposing the thermoelectricmaterial plates on the substrates.